Use of Interwire Ultrasonic Leakage to Quantify Loss of Prestress in Multiwire Tendons
Publication: Journal of Engineering Mechanics
Volume 137, Issue 5
Abstract
This paper presents a technique developed on the basis of ultrasonic guided waves to monitor prestress levels in multiwire prestressing strands. The transducer layout identified for stress measurement is composed of an ultrasound excitation provided by a piezoelectric element bonded on a peripheral wire. Ultrasound detection is performed on the central and peripheral wires at the strand’s end. The ultrasonic feature used for stress monitoring is the interwire leakage between the peripheral and the central wire, occurring across the strand anchorage. A semianalytical finite-element analysis is first used to predict modal and forced wave solutions in seven-wire strands as a function of the applied prestress level. The numerical analysis accounts for the changing interwire contact as a function of applied loads and predicts the attenuation occurring in loaded strand when the wave travels across the anchorage. Results of load monitoring in free strands during laboratory tests are then presented. Finally, a statistical approach is used to enhance the sensitivity of the technique to stress level in the strands. The study presented focuses on unbonded tendons. However, the final goal of the research is to monitor prestress loss in bonded tendons that are found in the majority of the bridges built in California.
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Acknowledgments
The strand monitoring project is funded at UCSD by the California Department of Transportation under contract # CADOT59A0538.
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© 2011 American Society of Civil Engineers.
History
Received: Oct 18, 2009
Accepted: Oct 22, 2010
Published online: Apr 15, 2011
Published in print: May 1, 2011
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